Question about extrusion multiplier... why would you adjust the extrusion multiplier rather than filament diameter? Does one change different outputs than the other? So far I've been able to get good quality by just dialing in filament diameter but I've never seen an explanation as to why there are two places to adjust.
Also, keep in mind that different filaments make a HUGE difference in print quality. Some rolls seem to churn out near perfect prints while others don't look as good or are less consistent. Filament quality and properties are still a big part of print issues. One time I struggled through an entire roll of filament before I figured out the problem was with that roll and not my printer. It about drove me crazy because I never considered the problem might be a bad batch of filament.